The influence of Theosophy on Lovecraft is quite clear and quite direct. Lovecraft was heavily influenced by the Theosophical tract The Story of Atlantis and the Lost Lemuria, a compilation of W. Scott-Elliot’s two brief works on Atlantis and Lemuria. Scott-Elliot, in turn, was explicating the work of H. P. Blavatsky. Thus, we can trace one strange little idea from Theosophy straight through to “The Call of Cthulhu.”

Here is Blavatsky’s Stanza XI of the second set of (her completely fake) Stanzas of Dzyan:

They built huge cities. Of rare earths and metals they built, and out of the fires vomited, out of the white stone of the mountains and of the black stone, they cut their own images in their size and likeness, and worshipped them.

Blavatsky, as her explication later in the Secret Doctrine(1888) shows, was thinking of Easter Island in writing this. W. Scott-Elliott picks up on this in his The Lost Lemuria (1904):

During the later part of the sixth, and the seventh sub-race they learnt to build great cities. These appear to have been of cyclopean architecture, corresponding with the gigantic bodies of the race. The first cities were built on that extended mountainous region of the continent which included, as will be seen in the first map, the present Island of Madagascar. Another great city is described in the "Secret Doctrine" as having been entirely built of blocks of lava. It lay some 30 miles west of the present Easter Island, and it was subsequently destroyed by a series of volcanic eruptions. The gigantic statues of Easter Island--measuring as most of them do about 27 feet in height by 8 feet across the shoulders--were probably intended to be representative not only of the features, but of the height of those who carved them, or it may be of their ancestors, for it was probably in the later ages of the Lemuro-Atlanteans that the statues were erected.

Now, here is Lovecraft in the “Call of Cthulhu”:

Old Castro remembered bits of hideous legend that paled the speculations of theosophists and made man and the world seem recent and transient indeed. There had been aeons when other Things ruled on the earth, and They had had great cities. Remains of Them, he said the deathless Chinamen had told him, were still be found as Cyclopean stones on islands in the Pacific. They all died vast epochs of time before men came, but there were arts which could revive Them when the stars had come round again to the right positions in the cycle of eternity. They had, indeed, come themselves from the stars, and brought Their images with Them.

Even the very word “cyclopean” derives from Theosophy, where Madame Blavatsky applied it generously to the Pacific islands, adopting and adapting the use from Ignatius Donnelly’s Atlantis, where that author had thoughtfully restricted it only to Greece and Mexico. Scott-Elliot picked it up in describing the lost city 30 miles west of Easter Island, and then Lovecraft adopted the same. Note, too, the interesting fact that the lost city of Theosophy’s ancient races is located in the empty part of the South Pacific; Lovecraft placed R’lyeh 20 degrees further west and 20 degrees further south, but retained the idea. In both cases, the cities were removed from the earth’s surface by geologic processes—volcanoes for Scott-Elliot, an unnamed sinking of the ocean floor for Lovecraft. (With Atlantis, Lemuria, and Mu all destroyed by volcanoes, I’m guessing Lovecraft found them a bit cliché.)